1987 COLEMAN MACH 3, A/C ONLY

When I plug in my camper the a/c comes on by itself, and goes off after running for 3 to 5 minutes. It will do this cycle as long as it is plugged in. If I push up on the selector knob ( fan, a/c, ect ) it will go off as long as I hold it. As soon as I let go it comes back on. I turned the thermostat so that the compressor won't come on, but it keeps doing the cycle. It started doing this about 3 weeks ago.

I don't think you need a new one just a good cleaning and service. The unit has a liquid high temperature line near the compressor with a fan blowing outside air across it this coil gets clogged over time with air-borne dirt and pollen and leaves and such and must be cleaned regularly or the unit will be unable to remove the heat from the coil and during the peak demand (3pm) the circuits that protect the compressor and the trailer wiring from being overloaded and burning or melting will trip. From what you have described it sounds like the RV is working as it should with a condenser coil that needs to be cleaned. GL and happy camping!P.S. I've only serviced the occasional RV unit but in those cases I laid a piece of plywood on top of the Rv for work platform removed the retaining screws from the top cover and used a spray bottle with a good heavy foaming cleaner a shop-vac and a brush to get the job done.

COLEMAN R.V. AIR CONDITIONER SERVICE AND REPAIR QUESTIONS
COLEMAN R.V. PRODUCTS
GO TO www.rvcomfort.com
Click on RVP (RV PRODUCTS)
Click on type of AC, if you can’t find the information you want there,
then click on contact us on the Green Bar.
You can get Service Support or Email address and Phone numbers.

“The voltage could be low – ”a) Check the voltage between #1 on theoverload switch and the “R” terminal of thecompressor while it is not humming. Thisvoltage must be 115 volts domestic USAmodels or 240 volts export/overseas models.No less than minus 10% is allowable.b) Check the voltage from “C” or “R” of thecompressor while it is humming (trying tostart). The latter reading will probably belower, but it still must be 103.5 voltsminimum domestic USA or 216 voltsminimum export/overseas models.If the first reading is above 103.5V domestic USA andthe second is under 103.5V domestic USA, there istoo much voltage drop in the lines - a situation whichmust be corrected for the air conditioner to performsafely and satisfactorily.2. “A capacitor could be shorted, weak or open.”Turn the power off.Caution – There is always a chance that a capacitor isholding a residual charge, so before touching aterminal, discharge the capacitor as explained earlierin this booklet.Remove capacitors, visually examine them and testthem per instructions given in earlier section oncapacitor testing (See page 9).If the capacitors test OK, replace them and carefullyreconnect the wires. Be sure the wires are connectedto the right terminals.3. “Start relay contacts could be open – ” if so equipped.Turn off all power, then check for continuity withohm meter between terminals 1 & 2.4. “Compressor start winding could be open orgrounded.”Check compressor windings per instructions. See thesection on the compressors (See page 8).5. “Compressor could be mechanically stuck.”This very rarely occurs and when it does, it is usuallyafter a lengthy shutdown. This should be consideredonly after all the above possible causes have beenpositively eliminated. To free a stuck compressor, useyour hermetic analyzer according to themanufacturers instructions.

The distance of the cord is a big deal, 10AWG Cord would be best for this situation. If you have a 50ft cord, make sure that the cord is not wound up on top itself as this can cause a drop in voltage and a spike in amperage. Is the compressor trying to come on at all? If not, then you may have a problem with the selector switch or the thermostat. If the compressor is humming for a few seconds and then stopping and then trying to come on again, it could be a problem with voltage loss. Anything below 98.5 plus or minus 10% is too low the for the compressor to kick on.

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if it is a programmable thermostat you can unhook thermostat and when it comes on select 3 instead of 1. As it sounds as though it is short cycling this happens in older houses with drafts. Hope this helps Tim

COLEMAN R.V. AIR CONDITIONER SERVICE AND REPAIR QUESTIONS
COLEMAN R.V. PRODUCTS
GO TO rvcomfort.com
Click on RVP (RV PRODUCTS)
Click on type of AC, if you can’t find the information you want there,
then click on contact us on the Green Bar.
You can get Service Support or Email address and Phone numbers.

Did you purchase a new Ducted Ceiling Unit with the Upper Unit air conditioner? If you are replacing an older mach 3, the ducted ceiling packs are not compatible and you will need to purchase the ceiling pack as well. The ducted ceiling pack part number for the 8333 series Mach III AC is below.

The distance of the cord is a big deal, 10AWG Cord would be best for this situation. If you have a 50ft cord, make sure that the cord is not wound up on top itself as this can cause a drop in voltage and a spike in amperage. Is the compressor trying to come on at all? If not, then you may have a problem with the selector switch or the thermostat. If the compressor is humming for a few seconds and then stopping and then trying to come on again, it could be a problem with voltage loss. Anything below 98.5 plus or minus 10% is too low the for the compressor to kick on.

I don't think you need a new one just a good cleaning and service. The unit has a liquid high temperature line near the compressor with a fan blowing outside air across it this coil gets clogged over time with air-borne dirt and pollen and leaves and such and must be cleaned regularly or the unit will be unable to remove the heat from the coil and during the peak demand (3pm) the circuits that protect the compressor and the trailer wiring from being overloaded and burning or melting will trip. From what you have described it sounds like the RV is working as it should with a condenser coil that needs to be cleaned. GL and happy camping!P.S. I've only serviced the occasional RV unit but in those cases I laid a piece of plywood on top of the Rv for work platform removed the retaining screws from the top cover and used a spray bottle with a good heavy foaming cleaner a shop-vac and a brush to get the job done.